Our project, Smart Fertilizer & Profitability Advisor (SFPA), is an IoT- and AI-driven decision support system that optimizes both soil nutrition and farm profitability. Building on real-time soil sensing (pH, moisture, nitrogen, phosphorus, potassium, calcium, temperature), our platform connects low-cost field nodes (e.g., NodeMCU/ESP8266 + NPK/pH/moisture sensors) to a cloud backend that ingests, validates, and stores time-stamped measurements. A nutrient optimization engine translates these measurements into crop-specific fertilizer recommendations, type, timing, and quantity, using agronomic ranges, site-specific historical responses, and rule-augmented machine learning to minimize nutrient imbalance, leaching risk, and input waste. In parallel, a profitability advisor integrates dynamic market signals (local farm-gate prices, transport and input costs) with yield response models to rank candidate crops by expected gross margin under the recommended nutrient plan. The system surfaces clear, actionable guidance—e.g., Plant Carrots: apply 18–22 kg/ha N in two splits; expected yield +12–18%, projected profit +RWF X/ha, through a mobile/web interface with offline caching and SMS fallbacks.

Technically, the platform comprises (i) edge devices performing basic calibration checks and batching, (ii) a secure API and data pipeline feeding a feature store, (iii) optimization modules that couple soil–crop response curves with cost functions, and (iv) explainable recommendations that justify each dose and crop ranking against sensed values and agronomic thresholds. We evaluate SFPA on multi-season field data using nutrient-use efficiency, yield uplift, input cost reduction, and profit/ha as primary metrics, with A/B comparisons to farmer-practice baselines. For smallholders, this unifies “what to grow,” “how to feed the soil,” and “whether it pays,” reducing guesswork and improving returns while supporting sustainable nutrient management. Deployed initially in Rwanda, the system localizes defaults (soil classes, rainfall patterns, price sources) and supports Kinyarwanda/English interfaces. By coupling precision fertilization with market-aware crop selection in one loop, SFPA advances practical, explainable, and economically grounded precision agriculture for resource-constrained settings.